An ongoing study has been designed to elucidate the structure of the growth cones in the visual system of wild type and mutated forms of Drosophila melanogaster. In the current year ultrastructural studies of the developing visual system will be carried out. In addition in vitro studies of the attached eye-antennal plate and brain complex will be continued. It is planned that experimental chemical/physical perturbation of the various components of the system will yield information on the spatial and temporal components of the development process. Freeze fracture studies may also be employed to further understand the nature and development of such aspects of the system as membrane structure or the presence and nature of junctions. Limited exploration of mutated forms will be undertaken for comparative purposes.